Microstructure and manufacturing process thereof

ABSTRACT

It is an object of the present invention to attain a microstructure having a miniature continuous structure which has high throughput and has been processed with high accuracy. To achieve this, provided is a microstructure having a column-shaped structure and a slit-forming portion which extends in a side-face direction from a side face of the column-shaped structure, wherein the slit-forming portion has a plurality of slits aligned in parallel at an interval from 20 to 1,000 nm in a direction along a center axis of the column-shaped structure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a microstructure, and manufacturingprocess thereof, which is minute and has excellent molding precision.The present invention particularly relates to a process formanufacturing a microstructure which can be employed as an opticalelement.

2. Description of the Related Art

In recent years, microminiaturization, increasing precision andincreasing super-high-end performance for a variety of structures hasbeen progressing across a wide-range of technical fields, wherein forexample, a structure miniaturized to a dimension in the order ofnanometers (hereinafter referred to as a “microstructure”) has beensought after. Microstructures have been manufactured using variousprocesses in the past. Specific examples include the following.

-   (1) Utilization of a self-organized structure-   (2) An optical shaping method using a laser or a light confocus-   (3) A method for fabricating a three-dimensional structure using an    electron beam or ion beam.-   (4) Utilizing a semiconductor process-   (5) A nanoimprinting process

Here, (1) a self-organized structure, as disclosed in Japanese PatentLaid-Open No. 2002-023356 is a method which places a molecule capable ofself-organization at a specific site of an underlying layer, such as asubstrate, to form a highly oriented compound onto the substrate in anoriented manner through interaction with a molecule having an associatedfunctional group which can react with the molecule capable ofself-organization. (2) the optical shaping method, as disclosed inJapanese Patent Laid-Open No. 1995-329188, is a method for manufacturinga microstructure by irradiating ultraviolet rays or similar laser beamonto a liquid photosetting resin to thereby form a thin film, and thensuccessively laminating this thin film. (3) a method for fabricating athree-dimensional structure using an electron beam or ion beam, asdisclosed in Japanese Patent Laid-Open No. 1989-261601, is a method formanufacturing a microstructure by irradiating an intensity-modulatedelectron beam onto a resist film coated onto a substrate. (4) asemiconductor process is a method for forming a structure by repeatedlycarrying out the steps of forming a mask pattern by photolithography andremoving an exposed portion by etching. (5) nanoimprinting is a methodfor transcribing a template pattern onto a substrate by pressing thesubstrate with a template having a nano-size pattern.

However, in (1) a self-organized structure, the position of the portionwhich undergoes shape-processing and self-organization is restricted,thus making it difficult to attain a structure having a desired shape orposition. For (2) optical shaping method, since light is employed forthe resin curing, shape-processing of a structure in the order ofnanometers is difficult. Furthermore, when performing complete curing bya full-cure step after molding of the photosetting resin, the entirestructure shrinks from one to several percent, whereby molding of astructure with a high degree of precision is difficult. For (3) a methodfor fabricating a three-dimensional structure, the thickness that can beprocessed is restricted, whereby the degree of freedom for the shape ina thickness direction is small, and throughput is also small. For (4) asemiconductor process and (5) nanoimprinting process, since athree-dimensional structure is made by fabricating a planer structureand then building these planar structures up, a long time is requiredfor structure fabrication. Furthermore, since these techniques undergo anumber of steps, a high precision processing of structure is difficult.

Meanwhile, at pages 304 to 306 of Micromachine/MEMS Technology Outlook,a Bosch process is disclosed. The Bosch process is a type of processingmethod for silicon substrates, which etches a silicon substrate layer inits thickness direction by alternating between etching with SF₆ gas andforming a passivation film from C₄F₈ gas, whereby a minute andcontinuous structure can be attained.

SUMMARY OF THE INVENTION

The present invention was created with the above-described problems inmind, wherein it aims at obtaining a microstructure comprising a minutestructure which has a high throughput and in which shape-processing ispossible with high precision.

The invention also aims at providing an optical element having excellentoptical processing characteristics comprising a microstructure.

To resolve the above-described problems, the present invention ischaracterized by having the following structure. That is, the presentinvention relates to a microstructure comprising a column-shapedstructure and a slit-forming portion which extends in a side-facedirection from a side face of the column-shaped structure, wherein theslit-forming portion has a plurality of slits aligned in parallel atintervals from 20 to 1,000 nm in a direction along a center axis of thecolumn-shaped structure.

The present invention also relates to a process for manufacturing amicrostructure which comprises a column-shaped structure and aslit-forming portion which extends in a side-face direction from a sideface of the column-shaped structure, wherein the slit-forming portionhas a plurality of slits aligned in parallel in a direction along acenter axis of the column-shaped structure, the process comprising thesteps of:

-   -   (1) preparing a substrate which has a thickness greater than a        height of the column-shaped structure;    -   (2) providing a mask extending in a prescribed direction of an        upper face of the substrate which comprises a narrow-width        portion in a direction which intersects with the extending        direction for defining a portion to serve as the slit-forming        portion and a broad-width portion in a direction which        intersects with the extending direction for defining a portion        to serve as the column-shaped portion;    -   (3) forming two facing grooves by carrying out isotropic etching        on an upper face of the substrate by a reactive ion etching        method using SF₆ gas using the mask as a etching mask, and        excavating in a thickness direction at least a portion of both        sides opposing the extending direction of the mask of the upper        face of the substrate;    -   (4) covering the upper face of the substrate forming the grooves        with a passivation film formed by plasma reaction using C₄F₈        gas;    -   (5) providing apertures for connecting between grooves which are        faced sandwiching the narrow-width portion of the mask at least        below the narrow-width portion of the mask, by carrying out        isotropic etching on the upper face of the substrate covered        with the passivation film by a reactive ion etching method using        SF₆ gas; and    -   (6) repeating the steps (3) to (5) for aligning in parallel the        apertures in a thickness direction below the narrow-width        portion of the mask, to thereby attain the microstructure as        well as extending the grooves in a thickness direction of the        substrate.

According to the manufacturing process of the present invention, amicrostructure can be attained which has a high throughput and in whichthe shape has been processed with high precision. Furthermore, accordingto the manufacturing process of the present invention, the shape, sizeand intervals, etc of the connecting portions and the aperture can becontrolled easily. Therefore, a microstructure according to the presentinvention can be used in a wide variety of applications by utilizingsuch characteristic. The microstructure according to the presentinvention can be, in particular, used as an excellent optical element byutilizing its minuteness and the high precision of its processed shape.

According to the manufacturing process of the present invention, amicrostructure can be manufactured which is minute, has high throughputand which has a shape processed with high precision. Furthermore, sincecontrol of the manufacturing conditions is easy and the manufacturingsteps are simple, a microstructure can be manufactured in short timeusing a simple apparatus. Furthermore, according to the manufacturingprocess of the present invention, the mask formed on the manufacturingsubstrate may comprise at least one or more width-varying portions, andthe mask having a variety of shapes can be employed. Therefore, themanufacturing process of the present invention can have a high degree ofdesign freedom.

According to the manufacturing process of the present invention, byforming a plurality of width-varying portions in the mask, a structureof a slit-forming portion can be easily controlled. In addition, amicrostructure can be attained wherein an intended characteristic variesdepending on the position in the microstructure. According to themanufacturing process of the present invention, by forming awidth-varying portion at both ends of the mask, a structure can beformed wherein a slit-forming portion is sandwiched betweencolumn-shaped structures, whereby the slit-forming portion can beprotected from damage during manufacture.

Furthermore, if the microstructure according to the present invention isemployed as an optical element, the desired characteristics which arerequired to be an optical element can be exhibited by utilizing theminuteness and high precision of the shape. In addition, amicrostructure according to the present invention can exhibit even moreexcellent desired optical element characteristics by arranging theconnecting portions and the apertures (slits) in equal intervals in anaxial direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating one example of a process formanufacturing a microstructure according to the present invention;

FIG. 2 is a schematic view illustrating one example of a process formanufacturing a microstructure according to the present invention;

FIG. 3 is a schematic view illustrating one example of a process formanufacturing a microstructure according to the present invention;

FIG. 4 is a schematic view illustrating one example of a microstructureaccording to the present invention;

FIG. 5 is an electron microscope photograph illustrating one example ofa microstructure according to the present invention;

FIG. 6 is a schematic view illustrating one example of a microstructureaccording to the present invention;

FIG. 7 is an electron microscope photograph illustrating one example ofa microstructure according to the present invention;

FIG. 8 is a schematic view illustrating one example of a microstructureaccording to the present invention;

FIG. 9 is a schematic view illustrating one example of a microstructureaccording to the present invention;

FIG. 10 is a schematic view illustrating one example of a microstructureaccording to the present invention;

FIG. 11 is a view illustrating one example of a mask pattern used in theprocess for manufacturing a microstructure according to the presentinvention;

FIG. 12 is a schematic view illustrating one example of a branchingfilter according to the present invention;

FIG. 13 is a schematic view illustrating one example of a wire gridaccording to the present invention;

FIG. 14 is a diagram illustrating a mask pattern used and amicrostructure manufactured in examples;

FIG. 15 is a view illustrating one example of a mask pattern used in theprocess for manufacturing a microstructure according to the presentinvention.

FIG. 16 is a schematic view illustrating one example of a process formanufacturing a microstructure according to the present invention;

FIG. 17 is a schematic view illustrating one example of a process formanufacturing a microstructure according to the present invention; and

FIG. 18 is a schematic view illustrating one example of a process formanufacturing a microstructure according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(Process for Manufacturing a Microstructure)

A microstructure according to the present invention can be manufacturedby alternating between isotropic etching and process fabricating aprotective film on the entire etching surface. For example, whenfabricating a microstructure by using a silicon substrate, a Boschprocess (also called ASE: Advanced Silicon Etching) can be employed. ABosch process is process silicon etching which alternates betweenetching using SF₆ and fluorocarbon deposition using C₄F₈, thus enablingetching with high selectivity and a high aspect ratio to be realized.

One example of a process for manufacturing a microstructure according tothe present invention will now be described in detail with reference toFIG. 1. First, a substrate 11 having a thickness greater than the heightof the column-shaped structures is prepared. As the substrate, a siliconsubstrate or an SOI substrate is used, and a thermal oxidation film SiO₂is formed on a surface of the substrate. Narrow-width portion 33 isconnected with broad-width portion 32 via width-varying portion 31 inthis mask 12.

Then, substrate exposed portion 13 which is not covered by the mask isformed on the substrate by photolithography. FIG. 1 (a) and (b) areschematic views which illustrate this state, wherein FIG. 1 (a) is aview showing the substrate from an upper face in a thickness directionand FIG. 1 (b) is a cross-sectional view in the A-A′ direction of FIG. 1(a). (In FIG. 1, as one example, a mask is used having two width-varyingportions 31.) Although the mask 12 is not especially restricted, aresist mask or a SiO₂ film, for example, can be employed.

After this, a Bosch process is carried out. That is, using the mask onthe substrate as the etching mask, isotropic etching of the substrate bya reactive ion etching process using SF₆ gas, deposition of apassivation film by a plasma reaction using C₄F₈ gas and isotropicetching using SF₆ gas in the same manner as the initial isotropicetching are carried out a number of times. This will now be explained inmore detail.

First, in the initial isotopic etching, at least a mask-side portion ofexposed portion 13 of the substrate (an aperture formed on a portionhaving both sides sandwiching the mask in direction intersecting withdirection 14 along which the mask extends) is excavated in thicknessdirection of a substrate to form a pair of grooves 16 (FIG. 1 (d)).Viewed along a cross-section parallel to the substrate, these groves 16are formed in a shape which stretches over outline 13 of the mask. FIG.1 (c) to (e) are schematic views which illustrate this state, whereinFIG. 1 (c) is a view showing the substrate from an upper face in athickness direction, FIG. 1 (d) is a cross-sectional view in the A-A′direction of FIG. 1 (c) and FIG. 1 (e) is a cross-sectional view in theB-B′ direction of FIG. 1 (c).

As the isotropic etching proceeds, the pair of grooves 16 connectpartially and abut onto a width-varying portion within the mask, wherebyaperture 17 connecting (connecting in direction 15 intersecting withextending direction 14 of the mask) the opposing grooves and sandwichingthe narrow-width portion 33 below narrow-width portion 33, is formed.The portion where aperture 17 (slit) is formed is not limited to theportion below narrow-width portion 33. Depending on the shape of themask and etching conditions, the aperture may be formed in a formstretching from the lower part of narrow-width portion 33 to the lowerpart of width-varying portion 31. Furthermore, since the isotropicetching finishes before the pair of grooves 16 completely connect,connecting portion 18 which is not removed by the isotropic etching isformed directly below narrow-width portion 33.

Next, a fluorocarbon passivation film 19 using C₄F₈ is formed on thesubstrate by a CVD chemical vapor growth process. FIG. 2(a) to (c) areschematic views which illustrate this state, wherein FIG. 2(a) is a viewshowing the substrate from an upper face in a thickness direction, FIG.2(b) is a cross-sectional view in the A-A′ direction of FIG. 2(a) andFIG. 2(c) is a cross-sectional view in the B-B′ direction of FIG. 2(a).

Subsequently, in the same manner as the initial isotropic etching,isotropic etching is conducted by a reactive ion etching process. FIG.3(a) to (c) are schematic views which illustrate this state, whereinFIG. 3(a) is a view showing the substrate from an upper face in athickness direction, FIG. 3(b) is a cross-sectional view in the A-A′direction of FIG. 3(a) and FIG. 3(c) is a cross-sectional view in theB-B′ direction of FIG. 3(a). During this etching, since a voltage biasis being applied, passivation film 21 of the side wall of the initialgroove (side etching portion) is not removed by the etching, wherein thepassivation film in the horizontal direction of substrate ispreferentially removed. Etching then further proceeds in a thicknessdirection lower portion of the substrate to form grooves 20. Thesegrooves 20 connect partially below aperture 17, whereby aperture (slit)22 connecting the opposing grooves and sandwiching a narrow-widthportion of the mask, is formed. Because the isotropic etching finishesbefore grooves 20 completely connect, connecting portion 23 which wasnot removed by the etching is formed in the space between initiallyformed aperture 17 and aperture 22.

Next, the slit-forming portion can be fabricated by forming in parallela plurality of slits in a thickness direction (a direction along acenter axis of the column-shaped structure) of the substrate by carryingout isotropic etching and the passivation film deposition as illustratedin FIGS. 1 to 3. The number of times that such isotropic etching andpassivation film deposition are carried out is preferably at least twotimes or more, but the number of times is not especially restricted.

Furthermore, the other example of a process for manufacturing amicrostructure according to the present invention will now be describedin detail with reference to FIGS. 16 to 18. First, mask 12 is formed ona substrate 11 in the same manner as FIG. 1. Then, substrate exposedportion which is not covered by the mask is formed on the substrate byphotolithography. After this, a Bosch process is carried out. First, inthe initial isotopic etching using SF₆ gas, at least a mask-side portionof exposed portion of the substrate is excavated in thickness directionof a substrate (FIG. 16(c)). FIG. 16(a) to (c) are schematic views whichillustrate this state, wherein FIG. 16(a) is a view showing thesubstrate from an upper face in a thickness direction, FIG. 16(b) is across-sectional view in the A-A′ direction of FIG. 16(a) and FIG. 16(c)is a cross-sectional view in the B-B′ direction of FIG. 16(a).

Next, a fluorocarbon passivation film 19 using C₄F₈ gas is formed on thesubstrate by a CVD chemical vapor growth process. FIG. 17(a) to (c) areschematic views which illustrate this state, wherein FIG. 17(a) is aview showing the substrate from an upper face in a thickness direction,FIG. 17(b) is a cross-sectional view in the A-A′ direction of FIG. 17(a)and FIG. 17(c) is a cross-sectional view in the B-B′ direction of FIG.17(a).

Subsequently, isotropic etching is conducted by a reactive ion etchingprocess. As the isotropic etching proceeds, the pair of grooves 16connect partially and abut onto a width-varying portion within the mask,whereby aperture 17 connecting (connecting in direction 15 intersectingwith extending direction 14 of the mask) the opposing grooves andsandwiching the narrow-width portion 33 below the narrow-width portion33, is formed. FIGS. 18(a) and (b) are schematic views which illustratethis state, wherein FIG. 18(a) corresponds to a cross-sectional view inthe A-A′ direction of microstructure of FIG. 17(a) and FIG. 18(b)corresponds to a cross-sectional view in the B-B′ direction ofmicrostructure of FIG. 17(a). During this etching, since a voltage biasis being applied, passivation film of the side wall of the groove (sideetching portion) is not removed by the etching, wherein the passivationfilm in the horizontal direction of substrate is preferentially removedto thereby form grooves. These grooves connect partially, wherebyaperture (slit) connecting the opposing grooves and sandwiching anarrow-width portion of the mask, is formed. The isotropic etchingfinishes before grooves completely connect.

Thus, one aperture is formed by process of FIGS. 16 to 18. Next, theslit-forming portion can be fabricated by repeating process asillustrated in FIGS. 16 to 18.

The conditions for each isotropic etching and passivation filmdeposition may be the same or different. If these conditions are thesame, each of the connecting portions and the apertures (slits) have thesame shape and size, thus enabling the intervals in thickness directionof the substrate to be formed with high precision at equal intervals.Therefore, by forming the aperture intervals with high precision atequal intervals, a microstructure having intended characteristicsdepending on the purpose can be manufactured. On the other hand, if theconditions for each isotropic etching and passivation film depositionare changed, each of the connecting portions and the apertures (slits)have a different shape and size, whereby these intervals in thicknessdirection of the substrate are also different.

Next, once the isotropic etching is conducted to a desired depth in thesubstrate, etching is finished. This etching may be stopped before thegrooves penetrate the substrate, or may be conducted until penetratingthrough the substrate. If etching is stopped before the groovespenetrate the substrate, a microstructure formed on the substrate can beattained, while if etching is conducted until the grooves penetratethrough the substrate, only a microstructure can be attained. Thesubstrate thickness is preferably from 5 to 100 μm, and more preferablyfrom 10 to 50 μm.

Subsequently, a microstructure according to the present invention isformed by removing the remaining mask 12 and passivation film 19. Thismicrostructure is illustrated in FIG. 4(a). FIG. 4(b) is a perspectiveview illustrating only the connecting portions of the microstructure ofthe FIG. 4(a).

FIG. 4(c) is a cross-sectional view in the A-A′ direction of theconnecting portions of FIG. 4(b). The uppermost connecting portion 59(the connecting portion is uppermost in thickness direction of thesubstrate; corresponding to uppermost connecting portion 44 in FIG.4(a)) is composed of face 53 and face 54. Connecting portion 60(corresponding to the connecting portion second from the top among theconnecting portions 45 in FIG. 4(a)) is composed of face 54 and face 55.Connecting portion 58 (corresponding to the connecting portion thirdfrom the top among the connecting portions 45 in FIG. 4(a)) is composedof face 56 and face 57. While in the microstructure of FIG. 4(a), twoconnecting portions are formed below the connecting portion 58, theconnecting portions formed below connecting portion 58 of theseconnecting portions have the same shape as connecting portion 58, andthe connecting portion formed at the lowermost part has the reverseshape to the uppermost connecting portion 59. Therefore, the twoconnecting portions formed below connecting portion 58 have been omittedfrom FIGS. 4(b) and (c).

An electron microscope photograph of an actually fabricatedmicrostructure is illustrated in FIG. 5. FIG. 5(a) is a photograph ofthe microstructure viewed from an oblique direction. FIG. 5(b) isenlarged view of slit-forming portions of the microstructure of FIG.5(a). From the electron microscope photograph of FIG. 5, it can beunderstood that a periodic structure is formed with excellent precision.

In the manufacturing process according to the present invention, themask to be used is not restricted to the above-described masks. Bychanging the extending direction of mask, the shape and size of thewidth-varying portion, the position of the width-varying portion isformed in the mask, or the width of the narrow-width portion and thebroad-width portion, or adjusting the etching conditions, the shape,size and interval of connecting portions and slits of the microstructurecan be processed into a desired shape with excellent precision. Inaddition, a minute three-dimensional microstructure can be fabricated ata high throughput with good reproducibility.

The mask can be formed so as to extend in a prescribed direction, andmay comprise a single closed curve or have both ends open. The mask mayalso be a linear shape extending in a fixed direction, or a curved shapein which the extending direction changes. In addition, a plurality oflinear masks, curved masks or combination of these masks linked togetherare also preferable. Still further, the mask may branch into a pluralityof masks midway, or the plurality of masks branched out midway may belinked together. The branched mask and linked mask may each be closed oropen, and may also be linear or curved.

The width-varying portion is acceptable as long as its width varies. Inthe present specification, regardless of whether the width variation iscontinuous or discontinuous. If the width variation is continuous,viewed from extending direction of the mask, a portion where the widthincreases or decreases continuously is taken to be a width-varyingportion. Thus, if there are a portion where the width increasescontinuously and a portion where the width decreases continuously, eachof these width-varying portions independently compose the differentwidth-varying portions. For example, when the width changes in adiscontinuous step-like manner (e.g., FIG. 1 (a) 31), the width-varyingportion is linear in the direction perpendicular to the extendingdirection of the mask, and without any length in the extending directionof the mask (e.g. FIG. 1 (a) 14). The ratio by which the width of thewidth-varying portion varies is not especially restricted, and neitheris such shape especially restricted. A side portion of a width-varyingportion where the width continuously varies is constituted from a curveor a straight line. In such case, the curve may be concave or convex oran uneven shape. The width-varying portion may be constituted from asingle straight line having different slopes, or from a plurality ofstraight lines. Furthermore, these shapes may be plural or a combinedshape.

The narrow-width portion and the broad-width portion are connected via awidth-varying portion. That is, a portion having a narrow width istermed “narrow-width portion”, and a portion having a broad width istermed a “broad-width portion” of the mask formed on both sidessandwiching a width-varying portion. Thus, “narrow-width” and“broad-width” are relative terms, so that even the same portion of amask can be termed narrow-width or broad-width. For example, FIG. 15 isa diagram viewed from an upper part of a mask formed on a substrate in astep-like manner. The mask in FIG. 15 has width-varying portions 1501 to1503. Taking width-varying portion 1503 as a reference, masks 1506 and1507 exist on either side of the portion. Because mask 1506 is thebroader of the two masks 1506 and 1507, mask 1506 is the “broad-widthportion” and mask 1507 is the “narrow-width portion”. However, ifwidth-varying portion 1502 is taken as the reference, masks 1505 and1506 exist on either side of the portion. Because mask 1505 is thebroader of the two masks 1505 and 1506, mask 1505 is the “broad-widthportion” and mask 1506 is the “narrow-width portion”. That is, mask 1506is a “broad-width portion” if it takes width-varying portion 1503 as areference, and is a “narrow-width portion” if it takes width-varyingportion 1502 as a reference. Thus, “narrow-width portion” or“broad-width portion” are depends on the width-varying portion taken asa reference, so that even the same portion in a mask can be a“narrow-width portion” or a “broad-width portion”. Furthermore, the“narrow-width portion” and “broad-width portion” may have no length inthe extending direction (e.g. FIG. 1(a) 14) and be a straight line indirection intersecting with extending direction of mask (e.g. FIG. 9(a)904, FIG. 10(a) 1024), or may have a prescribed length in the extendingdirection of the mask.

For example, FIG. 8(a) is a drawing which illustrates one example of amask used in the present invention. In FIG. 8(a), reference numerals 81to 84 denote width-varying portions, and reference numerals 810, 820,830 and 840 denote narrow-width portions. Reference numerals 815, 825,835, 845 and 855 denote broad-width portions. When such mask is used, amicrostructure having a structure as shown in FIGS. 8(b) and (c) can bemanufactured. FIG. 8(b) is a cross-sectional view in the A-A′ directionof FIG. 8(a) and FIG. 8(c) is a perspective view illustrating only theconnecting portions of the microstructure of FIG. 8(a). Uppermostconnecting portion 811 and connecting portion 812 are formed belownarrow-width portion 810, uppermost connecting portion 821 andconnecting portion 822 are formed below narrow-width portion 820,uppermost connecting portion 831 and connecting portion 832 are formedbelow narrow-width portion 830 and uppermost connecting portion 841 andconnecting portion 842 are formed below narrow-width portion 840.

As can be understood from FIG. 8, if the width ratio of the narrow-widthportion to the broad-width portion becomes increasing, the groove formedin the region including the mask aperture portion becomes bigger, andthe height H and width W′ of the uppermost connecting portion and theconnecting portions becomes smaller. If the width ratio of thenarrow-width portion to the broad-width portion becomes decreasing, thegroove formed in the region including the mask aperture portion becomessmaller and the height H and width W′ of the uppermost connectingportion and the connecting portions becomes larger. Furthermore, if thelength L of the narrow-width portion becomes longer, the length L′ ofthe uppermost connecting portion and the connecting portions alsobecomes longer, and if the length L of the narrow-width portion becomesshorter, the length L′ of the uppermost connecting portion and theconnecting portions also becomes shorter. (Thus, by adjusting the heightH of the uppermost connecting portion and the connecting portions, theintervals between the parallel slits can also be adjusted.)

A mask as illustrated in FIG. 9 can also be used. FIG. 9(a) is a drawingwhich illustrates one example of a mask used in the present invention.FIG. 9(b) is a cross-sectional view in the A-A′ direction of themicrostructure of FIG. 9(a) and FIG. 9(c) is a perspective viewillustrating only the connecting portions of the microstructure of FIG.9(a). In FIG. 9(a), reference numerals 91 and 94 to 96 denotewidth-varying portions. The sides of the width-varying portions 91, 94and 96 are constituted from a straight line, and a side portion ofwidth-varying portion 95 is partially constituted from a curve.Furthermore, reference numerals 901 to 904 denote narrow-width portionsand reference numerals 905 to 909 denote broad-width portions. Uppermostconnecting portion 92 and connecting portions 93 are mainly formed belowwidth-varying portion 91, uppermost connecting portion 97 and connectingportions 98 are mainly formed below two width-varying portions 94,uppermost connecting portion 99 and connecting portions 100 are mainlyformed below two width-varying portions 95 and structure 101 is mainlyformed below two width-varying portions 96.

When a microstructure is manufactured using the width-varying portion 91from FIG. 9, the height and width of connecting portions 92 and 93 areat a minimum at one end 901. Furthermore, when a microstructure ismanufactured using width-varying portions 94 and 95, the height andwidth of connecting portions 97 to 100 are at a minimum at centers 902and 903 in extending direction 14. When a width-varying portion 96 isused, the height and width of connecting portion 101 is at a minimum atcenter 904 in extending direction 14. (In the case of reference numeral101 in FIG. 9(c), a portion of the column-shaped structure is alsoincluded in the drawing.)

Thus, height H and width W′ of the connecting portions corresponding tothe broad-width portions of the mask become larger, and the height H andwidth W′ of the connecting portions corresponding to the narrow-widthportions of the mask become smaller. Furthermore, if the width W of thewidth-varying portions is dramatically varied, the portionscorresponding to the connecting portions also dramatically vary.

FIG. 10(a) is a drawing which illustrates the other example of a maskused in the present invention. Reference numerals 1010 to 1013 denotewidth-varying portions, reference numerals 1021 to 1024 denotenarrow-width portions, and reference numerals 1031 to 1035 denotebroad-width portions. FIG. 10(b) is a cross-sectional view in the A-A′direction of the microstructure of FIG. 10(a) and FIG. 10(c) is aperspective view illustrating only the connecting portions of themicrostructure of FIG. 10(a). The width-varying portions of FIG. 10(a)differ from the width-varying portions of FIG. 8(a) and FIG. 9(a) inthat the broad-width portions and narrow-width portions of thewidth-varying portions are aligned along face 1014. Uppermost connectingportion 1001 and connecting portions 1002 are formed below narrow-widthportion 1021, uppermost connecting portion 1003 and connecting portions1004 are formed below narrow-width portion 1022, uppermost connectingportion 1005 and connecting portions 1006 are mainly formed belowwidth-varying portion 1012 and uppermost connecting portion 1007 andconnecting portions 1008 are mainly formed below width-varying portion1013.

Furthermore, a mask having the same shape as that shown in FIG. 11 canbe used as the mask. In the masks of FIG. 11 (a) and (c), the mask isclosed, while the mask of FIG. 11 (b) is open. Furthermore, in the masksof FIG. 11 (a) and (b), a width-varying portion is formed at theirrespective apex.

Thus, even if a microstructure is manufactured using masks having avariety of shapes, a narrow-width portion is formed in at least onelocation, so that a connecting portion and an aperture is formed atleast below this portion by isotropic etching.

While the number of width-varying portions, narrow-width portions andbroad-width portions formed in the mask is not especially restricted, atleast one or more need to be formed. In addition, while the position ofthese width-varying portions, narrow-width portions and broad-widthportions in the mask is not especially restricted, for an open mask,these portions are preferably formed so that the broad-width portion isat both ends. More preferably, the broad-width portion is formed at bothends of the mask and at a portion sandwiched by both ends of the mask.By forming a broad-width portion at both ends of the mask, theslit-forming portion can be sandwiched by a column-shaped structure, tothereby prevent damage to the slit-forming portion. Furthermore, by alsoforming a broad-width portion at portions other than both ends, amicrostructure can be attained having apertures with high precision andhigh surface area density in the slit-forming portion.

When forming a plurality of width-varying portions, narrow-widthportions and broad-width portions, their length in extending directionof the mask is not especially restricted, and may be set freely.Preferably, all these portions are made to have the same length. Forexample, FIG. 6(b) illustrates a microstructure manufactured using amask having a plurality of the width-varying portions 31, narrow-widthportions 33 and broad-width portions 32 shown in FIG. 6(a). Using such amask, by carrying out isotropic etching and passivation film depositionby plasma reaction using C₄F₈ gas in the same manner as that describedabove, a microstructure is formed having four column-shaped structures61 aligned in a prescribed direction, and slit-forming portions 62 inthe space adjacent to column-shaped structures 61. On each slit-formingstructure 62 are formed an uppermost bridge structure (an uppermostconnecting portion) 64, three apertures 63 and three bridge-shapedstructures (connecting portions) 65.

Furthermore, an electron microscope photograph of a microstructureactually fabricated using such a mask is shown in FIG. 7. (In FIG. 7, asone example, two microstructures are illustrated, wherein the closermicrostructure has been fabricated as far as a middle portion in thephotograph.) From FIG. 7 it can be understood that the apertures and theconnecting portions in the slit-forming portion are aligned with uniformintervals.

The isotropic etching and passivation film deposition of steps (3) and(5) can be carried out using conventionally-known Bosch processoperation conditions.

The substrate is not restricted to being a silicon substrate or a SOIsubstrate. Substrates made from a variety of materials can be employed.For example, when using a substrate made from SiO₂, as the isotropicetching conditions, it is preferable to carry out isotropic etchingusing anhydrous HF vapor, and as the passivation film depositionconditions, it is preferable to set conditions in the same manner asthose described above.

(Microstructure)

The microstructure according to the present invention has at least onecolumn-shaped structure and a slit-forming portion which extends in aside face direction (direction intersecting with an axis direction ofthe column-shaped structure) from a side face of the column-shapedstructure. The slit-forming portions has a plurality of slits which arealigned in intervals from 20 to 1,000 nm in a direction along the centeraxis of the column-shaped structure, and are minute and excellent inshape uniformity. By utilizing these characteristics of being minute andexcellent in shape uniformity, the microstructure according to thepresent invention can be used across a wide range of fields, and can beused, for instance, as a filter for optical telecommunications. In sucha case, by setting the intervals between slits (slit period) to be 20 nmor more, filtering in the visible light region becomes possible.Furthermore, by setting to 1,000 nm or less, transmission loss islessened and filtering is possible as far as the telecommunicationswaveband (wavelength of 2 μm or less). Although the interval betweenslits corresponds to the height H of the connecting portions or theuppermost connecting portion in the direction along the center axis ofthe column-shaped structure, if the height H of the connecting portionsor the uppermost connecting portion is varied in the length direction ofthe connecting portions or the uppermost connecting portion, the heightof any portion can be taken as the slit interval.

The slits may be aligned with a fixed interval, or with two kinds ofinterval therebetween (The slits can have a first interval and a secondinterval). In such case, the intervals between the slits may be alignedso as to alternate between the first interval and the second interval,or may be aligned with the first intervals in a prescribed region, andwith the second intervals in the other prescribed region. The slits mayalso be aligned with three or more different intervals. For example, astructure is also acceptable in which the intervals between the slitsgradually decrease in the direction along the center axis of thecolumn-shaped structures.

The interval between slits is preferably from 120 to 750 nm. Inaddition, slit thickness (width of a slit in the direction along thecenter axis of the column-shaped structures) is also preferably aboutthe same width as the interval between slits.

FIG. 4 illustrates one example of a microstructure according to thepresent invention. The microstructure comprises two column-shapedstructures 41 and a slit-forming portion 42 formed between adjacentcolumn-shaped structures. As seen from an axial direction 43 of thecolumn-shaped structures, slit-forming portions 42 alternately haveconnecting portions (44 and 45) and a slit 46 (wherein the slits arealigned at a prescribed interval).

Here, “column-shaped structure” is defined as a portion which does notmanifest any slits in its cross-section when viewed from face parallelin an axial direction of the microstructure and perpendicular to thealigned direction 14 of the column-shaped structures. That is, in FIG.4(a), the portions of cross-section 48 and 49 does not manifest anyslits in its cross-section, and is thus a column-shaped structure whenviewed from face parallel in an axial direction of the microstructureand perpendicular to the aligned direction 14 of the column-shapedstructures. A “connecting portion” is defined as a structure whichconnects a portion of a side face of adjacent column-shaped structures41, a portion which manifests any slits in its cross-section when viewedfrom face parallel in an axial direction of the microstructure andperpendicular to the aligned direction 14 of the column-shapedstructures. Seen from an axial direction, the connecting portion at theuppermost location is termed the uppermost connecting portion. Theuppermost connecting portion connects the uppermost face of acolumn-shaped structure (corresponding to the uppermost face of thesubstrate) with a part of a side face of a column-shaped structure. Theshape of the cross-section intersecting with the axial direction of thecolumn-shaped structure is mainly prescribed by the broad-width portionof the mask formed on an upper portion thereof.

The column-shaped structures of the microstructure of FIG. 4(a) areconstituted from a curved face. The shape of the pair of column-shapedstructures connected by a connecting portion may be such that theirheight H in an axial direction is the same and these structures is onthe same plane, and their shape is not especially restricted. Forexample, a column-shaped structure may include a concave face, a convexface or an uneven face on at least a part of the side face. For example,the height of the column-shaped structure is preferably from 1 to 20 μm,and more preferably from 2 to 12 μm. Maximum width of the column-shapedstructure is preferably from 150 nm to 3 μm, and more preferably from200 nm to 1 μm. Length of the column-shaped structure is preferably nogreater than twice the width, and more preferably is about the same asthe width. Due to the fact that the size of the column-shaped structure(height, length, width) is within these ranges, a microstructure can bemanufactured having desired characteristics depending on the intendeduse.

Uppermost connecting portion 59 in FIG. 4(b) is constituted fromuppermost face 50 viewed from axial direction 43 and two curved faces53. Looking towards the axial direction, the change in surface area ofthe cross-section perpendicular to axial direction 43 of the uppermostconnecting portion 59 reaches a maximum at uppermost face 50, andcontinuously decreases towards the lower side in the axial direction,becoming zero at passing bottommost portion 501. Furthermore, lookingtowards length direction 51, the change in surface area of thecross-section perpendicular to length direction 51 of uppermostconnecting portion 59 reaches a maximum at one end 502 in the lengthdirection, continuously decreases to reach a minimum at center 503 inlength direction, then continuously increases to reach a maximum atother end 502 in the length direction.

While the shape of the connecting portion is not especially restricted,the uppermost connecting portion is constituted from an uppermost faceand at least two or more curved faces. How many faces the faces otherthan the uppermost face are constituted from is dependent on the size ofwidth-varying portion of the mask initially formed and the width andposition etc. of the broad-width portions and narrow-width portions. Thecurved face may be concave, convex or uneven on its inner side.

In FIG. 4(b), connecting portion 60 is constituted from four faces 54and 55, and connecting portion 58 is constituted from four faces 56 and57.

Looking towards the axial direction 43, the change in surface area ofthe cross-section perpendicular to axial direction 43 of theseconnecting portions 60 and 58 reaches zero at uppermost portion 504,continuously increases towards the lower side in the axial direction toreach a maximum, then continuously decreases to reach zero at passingbottommost portion 505.

Furthermore, looking towards length direction 51, the change in thesurface area of cross-section perpendicular to length direction 51reaches a maximum at one end 506 in the length direction, continuouslydecreases to reach a minimum at center of a length direction, thencontinuously increases to reach a maximum at other end 507 in the lengthdirection.

While the shape of the connecting portion is not especially restricted,such portion may be constituted from a plurality of faces. How manyfaces the connection portion is constituted from is dependent on thesize of the width-varying portion of the mask initially formed, and thewidth and position etc. of the broad-width portions and narrow-widthportions. This curved face may be concave, convex or uneven on its innerside.

The faces other than the uppermost face of the uppermost connectingportion and each face of the connecting portions may be the same ordifferent. Furthermore, it is also acceptable to make only a part of theconnecting portions the same, while a part can be made different. Thus,to make the shape of each face the same, the etching conditions forforming each face and the deposition conditions of the passivation filmshould be made the same. Furthermore, to make the shape of each facedifferent, the etching conditions for forming each face and thedeposition conditions of the passivation film should be made different.

The maximum height of the connecting portions is preferably from 25 to200 nm, and more preferably from 25 to 150 nm. Length is preferably from2 to 20 times the width, and more preferably from 5 to 10 times thewidth. Maximum width is preferably from 50 to 500 nm, and morepreferably from 100 to 250 nm. Due to the fact that the size of theuppermost connecting portion and the connecting portions (maximumheight, length, maximum width) is within these ranges, a microstructurecan be manufactured having desired characteristics depending on theintended use.

The maximum height of the uppermost connecting portion is preferablyfrom 15 to 100 nm, and more preferably from 15 to 80 nm.

The slits are formed between the connecting portions in a slit-formingportion. Here, looking from the axial direction, a slit is constitutedfrom faces of adjacent connecting portions which face each other. Forexample, in the microstructure of FIG. 4, a slit is constituted fromface 53 of uppermost connecting portion 59 and face 54 of connectingportion 60. A slit is also constituted from face 55 of connectingportion 60 and face 56 of connecting portion 58.

The connecting portions and slits are preferably aligned in equalintervals in an axial direction. In such case, the alignment interval ispreferably from 100 nm and 1 μm, and more preferably from 120 and 750nm. Due to the fact that the alignment interval is within these ranges,a microstructure can be manufactured in which has the shape with highprecision and a high surface area density.

While FIG. 4 illustrates a microstructure in which two column-shapedstructures are formed on the ends, the number of column-shapedstructures included in the microstructure according to the presentinvention is acceptable as long as it is at least one, and the number ofsuch structures is not especially restricted. In the case of a pluralityof column-shaped structures, such structures may be aligned in astraight line in a prescribed direction, or may be aligned at random.The slit-forming portions are either formed on a side face of a singlecolumn-shaped structure, or between two column-shaped structures. When aplurality of column-shaped structures are formed, the slit-formingportions may be formed between two column-shaped structures adjacent toeach other, or may be formed on a side face of a single column-shapedstructure among a plurality of column-shaped structures. Furthermore, ona side face of a single column-shaped structure, three or moreslit-forming portions may be formed.

Even when three or more connecting portions are formed between a pair ofcolumn-shaped structures, or even when a connecting portion are formedbetween three or more column-shaped structures, connecting portions canbe formed having the same shape and size as the above-describedconnecting portion. Furthermore, even when forming a plurality ofmicrostructures, the connecting portions of these differingmicrostructures can be made the same shape and size as theabove-described connecting portions. Still further, among theseconnecting portions, it is also acceptable to make only a part of theconnecting portions the same, while a part can be made different.

The microstructure according to the present invention can be used as anoptical element because of its minuteness and due to the fact that themicrostructure can comprise connecting portions and apertures in whichthe intervals and shape are controlled with high precision. This willnow be described in more detail.

(Optical Element)

The following four different mechanisms can be employed as anapplication for an optical element of the microstructure according tothe present invention. They are:

-   (1) Structural birefringence-   (2) Guided-mode resonance-   (3) Wire grid-   (4) Periodic structure

The principles behind each mechanism will be briefly explained, and adevice applying such principles will be illustrated.

(1) Structural Birefringence

When the structure is sufficiently smaller than the wavelength of thelight to be used, the structure can be deemed to be located in a uniformelectromagnetic field. The refractive index in such case greatly differsfrom that where light is incident in the direction perpendicular to theslit-forming portion (e.g. direction 1000 in FIG. 4(a)), depending onthe incident polarization direction. The dielectric constant for TEwaves (transverse electric waves) having an electric field intersectingwith the slit direction (e.g. direction 14 in FIG. 4(a)) is expressedas:εTE=fε ₁+(f−1)ε₂Here, f denotes the volume fraction of the slit structure material, ε₁denotes the dielectric constant of the slit structure material and ε₂denotes the refractive index of the medium.

In contrast, the dielectric constant for TM waves (transverse magneticwaves) having an electric field parallel to the slit direction (e.g.direction 14 in FIG. 4(a)) is expressed as:1/εTE=f/ε ₁+(f−1)/ε₂

If slits are made from Si, and f is set to 0.5, the refractive index ofTE direction is n_(TE)=2.56 and the refractive index of TM isn_(TM)=1.36, whereby birefringence can be achieved that could not beachieved using conventional materials.

Wave Plate

Providing the slit thickness (e.g. thickness of direction 1000 in FIG.4(a)) in accordance with the wavelength to be used allows ½ wave and ¼wave plates to be fabricated. Applying birefringence of this magnitudeenables the following self-standing type optical element to be achieved.

Polarized Beam Splitter

By combining a slit having a period λ1 which is sufficiently smallerthan the wavelength with a slit having a period λ2 which diffracts thelight wavelength to be used, a polarized beam splitter can be formed.That is, portions having a large polarization dependency is formed byλ1, and a grading of λ2 is formed by these portions. Although TE wavesare diffracted because of grading of λ2, a polarized beam splittertransmitting TM waves can be fabricated from a self-standing typemicrostructure. The period is preferably no greater than 1/10 of theintended wavelength.

High-Efficiency Diffraction Grating

Gradually varying the period λ1 in the polarized beam splitter enablesthe diffraction efficiency to be increased.

(2) Guided-Mode Resonance

When the slit period is about the same as the wavelength of the light tobe used, a guided-mode is formed in the slit. In the microstructureaccording to the present invention, the interval between slits (period)is from 20 to 1,000 nm. By setting the interval between slits to be from20 to 1,000 nm, filtering of a broad waveband is possible from thewaveband used in telecommunications (wavelength of 2 μm or less) throughto visible light, whereby a reflective type filter can be attained inwhich transmission loss is small.

(3) Wire Grid

By coating a metal over the surface of a slit made from Si, a wire gridstructure can be attained. When forming a wire grid structure, the wiregrid can be formed by depositing a metal layer by a well-knowndeposition method onto a microstructure manufactured in accordance withthe manufacturing process according to the present invention. As adeposition method, for example, CVD method and sputtering method can beemployed.

When the slit period is sufficiently smaller than the wavelength of thelight to be used (generally P (period)/λ (wavelength)<0.1), TE waves aretransmitted through and TM waves are reflected. By employing such astructure, a polarized element can be realized. Further, by selecting anappropriate period, a low-pass filter of TM waves can be formed. Forexample, FIG. 13 illustrates one example of a wire grid according to thepresent invention. Of the TE waves and TM waves that are incident fromdirection 1301, in the microstructure according to the present inventionTM waves are reflected, and only TE waves are transmitted. Therefore, byemploying a microstructure according to the present invention, specificlinear polarization can be taken Out.

(4) Periodic Structure

Since a connecting portion and an aperture have a periodic structuretoward a axial direction in the microstructure according to the presentinvention, when light is incident parallel to a slit-forming portion(e.g. direction 14 in FIG. 4(a)), a variety of filters can be formed.The periodic structure can be designed using the same design method asthat for a thin-film dielectric filter. The thickness of microstructuredirection 14 is from 20 to 1000 nm, when the microstructure is made fromSi in combination with using air for the void portion of themicrostructure, such as the slits.

As explained above, by using a microstructure according to the presentinvention, most kinds of optical element can be attained. Thecombination of such a microstructure with an optical waveguide canrealize the following optical device in a compact form and at low cost.

(Dispersion Compensator)

The refractive index of all optical materials such as glass changesaccording to wavelength, which is called wavelength dispersion. In longdistance optical multiplexing telecommunication, transmission timevaries depending on wavelength as a consequence of this refractive indexwavelength dispersion, which becomes a problem. To prevent this, atechnique called dispersion compensation is used which connects in thetransmission path devices having dispersion characteristics opposite tothose of the wavelength dispersion Qf the optical fiber. A dispersioncompensator is realized to control wavelength dispersion having anequivalent refractive index in accordance with a structure in adielectric multilayer film. The control of equivalent refractive indexis also possible in the microstructure according to the presentinvention in accordance with its structure, whereby a dispersioncompensator can be formed.

(Branching Filter)

A branching filter can be formed by making a narrow-band reflectionfilter utilizing guided-mode resonance align in one row at anappropriate angle (preferably 45°) toward the waveguide and optimizingthe filter structure in accordance with the extracted wavelength. FIG.12 illustrates one example of a branching filter according to thepresent invention. Incident light consisting of wavelengths λ3 to λ6 isbranched by filters 1201 to 1203 into light of respective wavelengths λ3to λ6.

EXAMPLE 1

Thermal oxidation was performed on a p-type silicon substrate having anorientation of (100) planes, to thereby form a 50 nm silicon oxide filmon the substrate surface. Subsequently, a negative-type EB resist, Calix(6) arena 3 weight % solution, was coated onto the silicon oxide film ata substrate revolution speed of 4,000 rpm using a spin coater. Thecoated film was baked at a temperature of 100° C. for 1 hour. Next, thepattern shown in FIG. 14(a) was formed on the baked film using anelectron beam lithography system (JEOL-5FE; manufactured by JEOL). FIG.14(b) is an enlarged SEM photograph of a part of the resist mask patternof FIG. 14(a). A Rainbow 4500 (manufactured by Lam Research Corporation)apparatus was then used to transcribe a resist mask pattern onto thesilicon oxide film under conditions of CF₄: CHF₃: Ar=20:10:150 sccm, 150mTorr, RF 200 W, 10° C. and 15 seconds. Next, using a MULTIPLEX-ICP(manufactured by Sumitomo Precision Products Co., Ltd.), silicon etchingand passivation film formation as 1 cycle were carried out by a Boschprocess at 20° C. for 20 cycles. The conditions at this time are shownin Table 1. TABLE 1 C₄F₈ Gas SF₆ Gas Gas Substrate Time PressureConcentration Concentration Impressed Impressed Treatment (s) (Pa)(SCCM) (SCCM) Power (W) Power (W) Etching 7 16 35 90 500 30 PassivationFilm 5 16 190 0 350 0 Formation

The silicon oxide film and passivation film were subsequently removed,to thereby manufacture a microstructure according to the presentinvention. The microstructure showed a shape as illustrated in FIG.14(c) and had a connecting portion as illustrated in FIG. 14(d). Theconnecting portion of the microstructure was height 20 nm, width 70 nmand length 650 nm. The aperture of the microstructure was height 100 nm,width 70 nm and length 650 nm.

1. A microstructure comprising a column-shaped structure and aslit-forming portion which extends in a side-face direction from a sideface of the column-shaped structure, wherein the slit-forming portionhas a plurality of slits aligned in parallel at intervals from 20 to1,000 nm in a direction along a center axis of the column-shapedstructure.
 2. An optical element comprising the microstructure accordingto claim
 1. 3. The optical element according to claim 2, wherein asurface is covered with a metal layer.
 4. The optical element accordingto claim 2 or 3, wherein the intervals of the slit in a direction alonga center axis of the column-shaped structure are constant.
 5. An opticalfilter using the optical element according to any of claims 2 or
 3. 6. Abranching filter comprising the optical filter according to claim
 5. 7.The optical element according to claim 2 or 3, wherein the slit-formingportion comprises slits aligned in parallel at a first interval andslits aligned in parallel at a second interval in a direction along acenter axis of the column-shaped structure.
 8. The optical elementaccording to claim 7, wherein a ratio of the first interval to thesecond interval is from 1:5 to 1:20.
 9. A polarized beam splitter usingthe optical element according to claim
 8. 10. A process formanufacturing a microstructure which comprises a column-shaped structureand a slit-forming portion which extends in a side-face direction from aside face of the column-shaped structure, wherein the slit-formingportion has a plurality of slits aligned in parallel in a directionalong a center axis of the column-shaped structure, the processcomprising the steps of: (1) preparing a substrate which has a thicknessgreater than a height of the column-shaped structure; (2) providing amask extending in a prescribed direction of an upper face of thesubstrate which comprises a narrow-width portion in a direction whichintersects with the extending direction for defining a portion to serveas the slit-forming portion and a broad-width portion in a directionwhich intersects with the extending direction for defining a portion toserve as the column-shaped portion; (3) forming two facing grooves bycarrying out isotropic etching on an upper face of the substrate by areactive ion etching method using SF6 gas using the mask as a etchingmask, and excavating in a thickness direction at least a portion of bothsides opposing the extending direction of the mask of the upper face ofthe substrate; (4) covering the upper face of the substrate forming thegrooves with a passivation film formed by plasma reaction using C4F8gas; (5) providing apertures for connecting between grooves which arefaced sandwiching the narrow-width portion of the mask at least belowthe narrow-width portion of the mask, by carrying out isotropic etchingon the upper face of the substrate covered with the passivation film bya reactive ion etching method using SF6 gas; and (6) repeating the steps(3) to (5) for aligning in parallel the apertures in a thicknessdirection below the narrow-width portion of the mask, to thereby attainthe microstructure as well as extending the grooves in a thicknessdirection of the substrate.
 11. The process for manufacturing amicrostructure according to claim 10, wherein the mask comprises aportion extending from one end to another end which is on an upper faceof the substrate, and the ends are the broad-width portions.
 12. Theprocess for manufacturing a microstructure according to claim 11,wherein the mask further comprises the broad-width portion on a portionother than on the end.
 13. The process for manufacturing amicrostructure according to any of claims 10 to 12, wherein the maskextends in a branched manner in a plurality of prescribed directions.14. The process for manufacturing a microstructure according to any ofclaims 10 to 12, wherein the substrate is an SOI substrate.
 15. Theprocess for manufacturing a microstructure according to any of claims 10to 12, wherein the steps (3) to (5) are finished prior to the groovespenetrating as far as a lower face of the substrate.